pentecost has 6 distinct synonyms spread across 2 of its 2 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
seventh Sunday after Easter; commemorates the emanation of the Holy Spirit to the Apostles; a quarter day in Scotland
(Judaism) Jewish holy day celebrated on the sixth of Sivan to celebrate Moses receiving the Ten Commandments
Synonyms, antonyms and the broader and narrower relations for pentecost come from Princeton University’s WordNet. Full sources and licences.